Catalyst treatment useful for aromatics conversion process

ABSTRACT

A process for preparing a transalkylation catalyst, the catalyst itself, and a transalkylation process for using the catalyst are herein disclosed. The catalyst comprises rhenium metal on a solid-acid support such as mordenite, which has been treated with a sulfur-based agent. Such treatment reduces the amount of methane produced by metal hydrogenolysis in a transalkylation process wherein heavy aromatics like A 9 + are reacted with toluene to produce xylenes. Reduced methane production relative to total light ends gas production results in lower hydrogen consumption and lower reactor exotherms.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation-In-Part of application Ser. No.10/855,463, filed May 27, 2004, now U.S. Pat. No. 7,220,885 the contentsof which are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

This invention relates to catalytic hydrocarbon conversion, and morespecifically to the use of a metal-stabilized solid-acid catalyst fortransalkylation of heavy aromatics such as C₉ ⁺ compounds with tolueneto produce xylenes. By pretreating a rhenium containing zeoliticcatalyst with sulfur, undesired methane formation is reduced.

BACKGROUND OF THE INVENTION

Xylene isomers, para-xylene, meta-xylene and ortho-xylene, are importantintermediates which find wide and varied application in chemicalsyntheses. Para-xylene upon oxidation yields terephthalic acid, which isused in the manufacture of synthetic textile fibers and resins.Meta-xylene is used in the manufacture of plasticizers, azo dyes, woodpreservers, etc. Ortho-xylene is feedstock for phthalic anhydrideproduction.

Xylene isomers from catalytic reforming or other sources generally donot match demand proportions as chemical intermediates, and furthercomprise ethylbenzene, which is difficult to separate or to convert.Para-xylene in particular is a major chemical intermediate with rapidlygrowing demand, but amounts to only 20 to 25% of a typical C₈ aromaticsstream. Among the aromatic hydrocarbons, the overall importance of thexylenes rivals that of benzene as a feedstock for industrial chemicals.Neither the xylenes nor benzene are produced from petroleum by thereforming of naphtha in sufficient volume to meet demand, and conversionof other hydrocarbons is necessary to increase the yield of xylenes andbenzene. Often toluene (C₇) is dealkylated to produce benzene (C₆) orselectively disproportionated to yield benzene and C₈ aromatics fromwhich the individual xylene isomers are recovered.

A current objective of many aromatics complexes is to increase the yieldof xylenes and to de-emphasize benzene production. Demand is growingfaster for xylene derivatives than for benzene derivatives. Refinerymodifications are being effected to reduce the benzene content ofgasoline in industrialized countries, which will increase the supply ofbenzene available to meet demand. A higher yield of xylenes at theexpense of benzene thus is a favorable objective, and processes totransalkylate C₉ and heavier aromatics with benzene and toluene havebeen commercialized to obtain high xylene yields.

U.S. Pat. No. 4,365,104 discloses a process for modifying ZSM-5 typezeolite catalysts with sulfur-based treating agents in order to enhancepara-selective catalyst properties based upon the molecular sieve.

U.S. Pat. No. 4,857,666 discloses a transalkylation process overmordenite and suggests modifying the mordenite by steam deactivation orincorporating a metal modifier into the catalyst.

U.S. Pat. No. 5,763,720 discloses a transalkylation process forconversion of C₉ ⁺ into mixed xylenes and C₁₀ ⁺ aromatics over acatalyst containing zeolites illustrated in a list including amorphoussilica-alumina, MCM-22, ZSM-12, and zeolite beta, where the catalystfurther contains a Group VIII metal such as platinum. Treatment toreduce aromatics loss by ring hydrogenation over such a catalystincludes sulfur exposure.

U.S. Pat. No. 6,060,417 discloses a transalkylation process using acatalyst based on mordenite with a particular zeolitic particle diameterand having a feed stream limited to a specific amount of ethylcontaining heavy aromatics. Said catalyst contains nickel or rheniummetal.

U.S. Pat. No. 6,486,372 discloses a transalkylation process using acatalyst based on dealuminated mordenite with a high silica to aluminaratio that also contains at least one metal component.

U.S. Pat. No. 6,613,709 discloses a catalyst for transalkylationcomprising zeolite structure type NES and metals such as rhenium,indium, or tin. The use of sulfur is disclosed, but Example 4 shows asulfurization step (called sulphurization) that is only performed on acatalyst C₂ containing nickel, which is described as ‘not in Accordancewith the Invention’. Also, nothing is disclosed about the effect ofsulfur on methane yield.

Many types of supports and elements have been disclosed for use ascatalysts in processes to transalkylate various types of aromatics intoxylenes, but the problem presented by high methane production associatedwith rhenium containing catalysts appears to have gone as yetunrecognized in the art. Applicants have found a solution with specificsulfur treatment of rhenium supported on solid-acid catalysts thatincreases yield of xylenes and decreases yield of undesired methane,which is associated with high metal hydrogenolysis activity. Avoidanceof high metal hydrogenolysis activity becomes especially important underconditions of low total hydrogen partial pressure.

SUMMARY OF THE INVENTION

A principal object of the present invention is to provide a process forpreparing a catalyst, the catalyst itself, and a process for thetransalkylation of alkylaromatic hydrocarbons into xylenes. Morespecifically, the present invention is directed to converting aromatichydrocarbons with decreased yields of methane. This invention is basedon the discovery that a sulfided catalyst based on a solid-acid materialin conjunction with a rhenium metal component exhibits decreased methaneproduction when contacted under transalkylation conditions.

Accordingly, a broad embodiment of the present invention is a processfor preparing a catalyst having a sulfur component, a rhenium component,and a solid-acid component. In another embodiment, the present inventionis a transalkylation process for using the catalyst to convert aromaticsinto xylenes with decreased methane production. In yet anotherembodiment, the present invention is the catalyst itself having asolid-acid component such as mordenite, mazzite, zeolite beta, ZSM-11,ZSM-12, ZSM-22, ZSM-23, MFI topology zeolite, NES topology zeolite,EU-1, MAPO-36, MAPSO-31, SAPO-5, SAPO-11, SAPO-41, and silica-alumina.The catalyst also has an essential rhenium metal component and a sulfurcomponent.

These, as well as other objects and embodiments will become evident fromthe following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effect of sulfiding rhenium catalyst on activity forthe transalkylation of C₇, C₉, and C₁₀ aromatics at a level of about 50wt-% conversion while producing C₈ aromatics.

FIG. 2 shows the effect of sulfiding rhenium catalyst on methane (C₁)selectivity, shown as wt-% of total C₁ to C₅ produced by the process.

DETAILED DESCRIPTION OF THE INVENTION

The feed stream to the present process generally comprises alkylaromatichydrocarbons of the general formula C₆H_((6−n))R_(n), where n is aninteger from 0 to 6 and R is CH₃, C₂H₅, C₃H₇, or C₄H₉, in anycombination. Suitable alkylaromatic hydrocarbons include, for examplebut without so limiting the invention, benzene, toluene, ethylbenzene,ethyltoluenes, propylbenzenes, tetramethylbenzenes,ethyl-dimethylbenzenes, diethylbenzenes, methylpropylbenzenes,ethylpropylbenzenes, triethylbenzenes, di-isopropylbenzenes, andmixtures thereof. The feed stream may comprise lower levels ofortho-xylene, meta-xylene, and para-xylene that are the desired productsof the present process.

The feed stream also may comprise naphthalene and other C₁₀ and C₁₁aromatics and suitably is derived from one or a variety of sources.Polycyclic aromatics such as the bicyclic components includingnaphthalene, methylnaphthalene, are permitted in the feed stream of thepresent invention. Indane, which is also referred to as indan or indene,is meant to define a carbon number nine aromatic species with one carbonsix ring and one carbon five ring wherein two carbon atoms are shared.Naphthalene is meant to define a carbon number ten aromatic species withtwo carbon six rings wherein two carbon atoms are shared. Polycyclicaromatics may also be present in amounts above the trace amountspermitted in prior art, and these amounts are herein defined assubstantial amounts such as greater than about 0.5 wt-% of the feedstream.

Feed components may be produced synthetically, for example, from naphthaby catalytic reforming or by pyrolysis followed by hydrotreating toyield an aromatics-rich product. The feed stream may be derived fromsuch product with suitable purity by extraction of aromatic hydrocarbonsfrom a mixture of aromatic and nonaromatic hydrocarbons andfractionation of the extract. For instance, aromatics may be recoveredfrom reformate. Reformate may be produced by any of the processes knownin the art. The aromatics then may be recovered from reformate with theuse of a selective solvent, such as one of the sulfolane type, in aliquid-liquid extraction zone. The recovered aromatics may then beseparated into streams having the desired carbon number range byfractionation. When the severity of reforming or pyrolysis issufficiently high, extraction may be unnecessary and fractionation maybe sufficient to prepare the feed stream. Such fractionation typicallyincludes at least one separation column to control feed end point.

The feed heavy-aromatics stream, characterized by C₉ ⁺ aromatics (or A₉⁺), permits effective transalkylation of light aromatics such as benzeneand toluene with the heavier C₉ ⁺ aromatics to yield additional C₈aromatics that are preferably xylenes. The heavy-aromatics streampreferably comprises at least about 90 wt-% total aromatics; and may bederived from the same or different known refinery and petrochemicalprocesses as the benzene and toluene, and/or may be recycled from theseparation of the product from transalkylation.

The feed stream is preferably transalkylated in the vapor phase and inthe presence of hydrogen. If transalkylated in the liquid phase, thenthe presence of hydrogen is optional. If present, free hydrogen isassociated with the feed stream and recycled hydrocarbons in an amountof from about 0.1 moles per mole of alkylaromatics up to 10 moles permole of alkylaromatic. This ratio of hydrogen to alkylaromatic is alsoreferred to as hydrogen to hydrocarbon ratio. The transalkylationreaction preferably yields a product having an increased xylene content.High yields of methane are undesired as they generally accompany highconsumption of hydrogen, high exotherms across a reactor, and maydecrease total yields of xylenes. High metal hydrogenolysis activitypresent in a rhenium containing catalyst causes a shift of light endsgases to even lighter gas species, specifically causing methane toincrease at the expense of ethane, propane, butane, and pentane. Such amethane increase consumes hydrogen and increases reactor exotherms, bothof which lead to economic problems associated with increased utilitiesfor heat and for hydrogen supply. Also, xylenes increase when totalhydrogen partial pressure is reduced relative to higher levels ofhydrogen; such relatively lower levels of total hydrogen, if any ispresent at all, favor reduced loss of aromatic rings by hydrogensaturation.

The feed to a transalkylation reaction zone usually first is heated byindirect heat exchange against the effluent of the reaction zone andthen is heated to reaction temperature by exchange with a warmer stream,steam or a furnace. The feed then is passed through a reaction zone,which may comprise one or more individual reactors. The use of a singlereaction vessel having a fixed cylindrical bed of catalyst is preferred,but other reaction configurations utilizing moving beds of catalyst orradial-flow reactors may be employed if desired. Passage of the combinedfeed through the reaction zone effects the production of an effluentstream comprising unconverted feed and product hydrocarbons. Thiseffluent is normally cooled by indirect heat exchange against the streamentering the reaction zone and then further cooled through the use ofair or cooling water. The effluent may be passed into a stripping columnin which substantially all C₅ and lighter hydrocarbons present in theeffluent are concentrated into an overhead stream and removed from theprocess. An aromatics-rich stream is recovered as net stripper bottomswhich is referred to herein as the transalkylation effluent.

To effect a transalkylation reaction, the present invention incorporatesa transalkylation catalyst in at least one zone, but no limitation isintended in regard to a specific catalyst other than such catalyst mustpossess a solid-acid component and a rhenium metal component. Conditionsemployed in the transalkylation zone normally include a temperature offrom about 200° to about 540° C. The transalkylation zone is operated atmoderately elevated pressures broadly ranging from about 100 kPa toabout 6 MPa absolute. The transalkylation reaction can be effected overa wide range of space velocities. Weight hourly space velocity (WHSV)generally is in the range of from about 0.1 to about 20 hr⁻¹.

The transalkylation effluent is separated into a light recycle stream, amixed C₈ aromatics product and a heavy recycle stream. The mixed C₈aromatics product can be sent for recovery of para-xylene and othervaluable isomers. The light recycle stream may be diverted to other usessuch as to benzene and toluene recovery, but alternatively is recycledpartially to the transalkylation zone. The heavy recycle stream containssubstantially all of the C₉ and heavier aromatics and may be partiallyor totally recycled to the transalkylation reaction zone.

Several types of transalkylation catalysts that may be used in thepresent invention are based on a solid-acid material combined with ametal component. Suitable solid-acid materials include all forms andtypes of mordenite, mazzite (omega zeolite), beta zeolite, ZSM-11,ZSM-12, ZSM-22, ZSM-23, MFI type zeolite, NES type zeolite, EU-1,MAPO-36, MAPSO-31, SAPO-5, SAPO-11, SAPO-41, and silica-alumina or ionexchanged versions of such solid-acids. For example, in U.S. Pat. No.3,849,340 a catalytic composite is described comprising a mordenitecomponent having a SiO₂/Al₂O₃ mole ratio of at least 40:1 prepared byacid extracting Al₂O₃ from mordenite prepared with an initial SiO₂/Al₂O₃mole ratio of less than 30:1 and a metal component selected from copper,silver and zirconium. Additional mordenite components suitable for useinclude those having a SiO₂/Al₂O₃ mole ratio of from about 13 to about19 with examples including Zeolyst mordenite CBV-10A which has aSiO₂/Al₂O₃ mole ratio of 13 and another mordenite having a SiO₂/Al₂O₃mole ratio in the range of about 17 to about 18.5 commercially availablefrom Tosoh. Refractory inorganic oxides, combined with theabove-mentioned and other known catalytic materials, have been founduseful in transalkylation operations. For instance, silica-alumina isdescribed in U.S. Pat. No. 5,763,720. Crystalline aluminosilicates havealso been employed in the art as transalkylation catalysts. ZSM-12 ismore particularly described in U.S. Pat. No. 3,832,449. Zeolite beta ismore particularly described in Re. 28,341 (of original U.S. Pat. No.3,308,069). A favored form of zeolite beta is described in U.S. Pat. No.5,723,710, which is incorporated herein by reference. The preparation ofMFI topology zeolite is also well known in the art. In one method, thezeolite is prepared by crystallizing a mixture containing an aluminasource, a silica source, an alkali metal source, water and an alkylammonium compound or its precursor. Further descriptions are in U.S.Pat. No. 4,159,282, U.S. Pat. No. 4,163,018, and U.S. Pat. No.4,278,565.

Other suitable solid-acid materials include mazzite, ZSM-11, ZSM-22,ZSM-23, NES type zeolite, EU-1, MAPO-36, MAPSO-31, SAPO-5, SAPO-11,SAPO-41. Preferred mazzite zeolites include Zeolite Omega. The synthesisof the Zeolite Omega is described in U.S. Pat. No. 4,241,036. ZSMintermediate pore size zeolites useful in this invention include ZSM-5(U.S. Pat. No. 3,702,886); ZSM-11 (U.S. Pat. No. 3,709,979); ZSM-12(U.S. Pat. No. 3,832,449); ZSM-22 (U.S. Pat. No. 4,556,477); ZSM-23(U.S. Pat. No. 4,076,842). European Patent EP 0378916 B1 describes NEStype zeolite and a method for preparing NU-87. The EUO structural-typeEU-1 zeolite is described in U.S. Pat. No. 4,537,754. MAPO-36 isdescribed in U.S. Pat. No. 4,567,029. MAPSO-31 is described in U.S. Pat.No. 5,296,208 and typical SAPO compositions are described in U.S. Pat.No. 4,440,871 including SAPO-5, SAPO-11 and SAPO-41.

A refractory binder or matrix is optionally utilized to facilitatefabrication of the catalyst, provide strength and reduce fabricationcosts. The binder should be uniform in composition and relativelyrefractory to the conditions used in the process. Suitable bindersinclude inorganic oxides such as one or more of alumina, magnesia,zirconia, chromia, titania, boria, thoria, phosphate, zinc oxide andsilica. Alumina is a preferred binder.

The catalyst also contains an essential rhenium metal component. Thiscomponent may exist within the final catalytic composite as a compoundsuch as an oxide, sulfide, halide, or oxyhalide, in chemical combinationwith one or more of the other ingredients of the composite. The rheniummetal component may be incorporated in the catalyst in any suitablemanner, such as coprecipitation, ion-exchange, co-mulling orimpregnation. The preferred method of preparing the catalyst involvesthe utilization of a soluble, decomposable compound of rhenium metal toimpregnate the carrier material in a relatively uniform manner. Typicalrhenium compounds which may be employed include ammonium perrhenate,sodium perrhenate, potassium perrhenate, potassium rhenium oxychloride,potassium hexachlororhenate (IV), rhenium chloride, rhenium heptoxide,perrhenic acid, and the like compounds. Preferably, the compound isammonium perrhenate or perrhenic acid because no extra steps may beneeded to remove any co-contaminant species. This component may bepresent in the final catalyst composite in any amount which iscatalytically effective, generally comprising about 0.01 to about 2 wt-%of the final catalyst calculated on an elemental basis.

The catalyst may optionally contain additional modifier metalcomponents. Preferred metal modifier components of the catalyst include,for example, tin, germanium, lead, indium, platinum, palladium andmixtures thereof. Catalytically effective amounts of such metalmodifiers may be incorporated into the catalyst by any means known inthe art. A preferred amount is a range of about 0.01 to about 2.0 wt-%on an elemental basis.

One shape of the catalyst of the present invention is a cylinder. Suchcylinders can be formed using extrusion methods known to the art.Another shape of the catalyst is one having a trilobal or three-leafclover type of cross section that can be formed by extrusion. Anothershape is a sphere that can be formed using oil-dropping methods or otherforming methods known to the art.

At least one oxidation step may be used in the preparation of thecatalyst. The conditions employed to effect the oxidation step areselected to convert substantially all of the metallic components withinthe catalytic composite to their corresponding oxide form. The oxidationstep typically takes place at a temperature of from about 370° to about650° C. An oxygen atmosphere is employed typically comprising air.Generally, the oxidation step will be carried out for a period of fromabout 0.5 to about 10 hours or more, the exact period of time being thatrequired to convert substantially all of the metallic components totheir corresponding oxide form. This time will, of course, vary with theoxidation temperature employed and the oxygen content of the atmosphereemployed.

In preparing the catalyst, a reduction step may optionally be employed.The reduction step is designed to reduce substantially all of the metalcomponents to the corresponding elemental metallic state and to ensure arelatively uniform and finely divided dispersion of this componentthroughout the catalyst. It is preferred that the reduction step takeplace in a substantially water-free environment. Preferably, thereducing gas is substantially pure, dry hydrogen (i.e., less than 20wt-ppm water). However, other gases may be present such as CO, nitrogen,etc. Typically, the reducing gas is contacted with the oxidizedcatalytic composite at conditions including a reduction temperature offrom about 315° to about 650° C. for a period of time of from about 0.5to 10 or more hours effective to reduce at least about 80 wt-%, or morepreferably substantially all of the rhenium metal component to theelemental metallic state. The preferred reduction conditions include atemperature of greater than about 400° C. for a time of greater thanabout 2.5 hours. The reduction step may be performed under atmosphericpressure or at higher pressures. The reduction step may be performedprior to loading the catalytic composite into the hydrocarbon conversionzone or it may be performed in situ as part of a hydrocarbon conversionprocess start-up procedure. However, if this latter technique isemployed, proper precautions must be taken to pre-dry the conversionunit to a substantially water-free state, and a substantially water-freereducing gas should be employed.

Finally, the catalytic composite is subjected to an essential sulfurtreatment or pre-sulfiding step. The sulfur component may beincorporated into the catalyst by any known technique. Any one or acombination of in situ and/or ex situ sulfur treatment methods ispreferred. The resulting catalyst mole ratio of sulfur to rhenium ispreferably from about 0.1 to less than about 1.5, and even morepreferably the catalyst mole ratio of sulfur to rhenium is about 0.3 toabout 0.8.

A catalyst pretreatment ex situ is one method for minimizing the methaneproduction of the catalyst composition by exposing it to sulfur.Effective treatment is accomplished by contacting the catalyst with asource of sulfur at a temperature ranging from about 0° to about 500°C., with room temperature providing satisfactory results. The source ofsulfur can be contacted with the catalyst directly or via a carrier gas,typically, an inert gas such as hydrogen or nitrogen. In thisembodiment, the source of sulfur is typically hydrogen sulfide. Forexample, the treatment medium may contain from about 10 to about 100% ofhydrogen sulfide.

The catalyst composition can also be treated in situ where a source ofsulfur is contacted with the catalyst composition by adding it to thehydrocarbon feed stream in a concentration ranging from about 0.1 ppmwsulfur to about 10,000 ppmw sulfur. In one embodiment, the concentrationis in the range of 100 to 500 ppmw sulfur in the hydrocarbon stream, andin another embodiment the concentration is greater than 0.1 ppmw, and inyet another embodiment the concentration is greater than 1 ppmw. Theneed to add a sulfur source to the hydrocarbon feed stream may bereduced or eliminated entirely depending on the actual content of sulfurwhich may already be present in some hydrocarbon streams. Any sulfurcompound that will decompose to form H₂S and, optionally, a lighthydrocarbon at about 500° C. or less will suffice. Typical examples ofappropriate sources of sulfur include carbon disulfide and alkylsulfidessuch as methylsulfide, dimethylsulfide, dimethyldisulfide,diethylsulfide and dibutylsulfide. Typically, sulfur treatment isinitiated by incorporating a source of sulfur into the feed andcontinuing sulfur treatment for a few days, typically, up to 10 days,more specifically, from one to five days. The sulfur treatment may bemonitored by measuring the concentration of sulfur in the product offgas. The time calculated for sulfur treatment will depend on the actualconcentration of sulfur in the feed and the desired sulfur loading to beachieved on the catalyst. Furthermore, the concentration of sulfur inthe feed can be modified to achieve the desired sulfur loading on thecatalyst in a determined amount of time. Shorter times will requirehigher concentrations of sulfur.

The catalyst can be contacted with sulfur during service by co-feedingsulfur to the reactor in varied amounts via the hydrogen stream enteringthe reactor or the hydrocarbon feedstock. The sulfur can be continuouslyadded to the feedstock throughout the process cycle or the sulfur can beintermittently continuously added in which this sulfur is co-fedcontinuously for a period of time, discontinued, then co-fed again.

EXAMPLES

The following examples are presented only to illustrate certain specificembodiments of the invention, and should not be construed to limit thescope of the invention as set forth in the claims. There are manypossible other variations, as those of ordinary skill in the art willrecognize, within the scope of the invention.

Example 1

Samples of catalysts comprising mordenite were prepared for comparativepilot-plant testing by the forming process called extrusion. Typically,2500 g of a powder blend of 25 wt-% alumina (commercially availableunder the trade names Catapal™ B and/or Versal™ 250) and 75 wt-%mordenite (commercially available under the trade name Zeolyst™ CBV-21A)was added to a mixer. A solution was prepared using 10 g nitric acid(67.5 wt-% HNO₃) with 220 g deionized water and the solution wasstirred. The solution was added to the powder blend in the mixer, andmulled to make dough suitable for extrusion. The dough was extrudedthrough a die plate to form cylindrically shaped (0.16 cm diameter)extrudate particles. The extrudate particles were calcined at about 565°C. with 15 wt-% steam for 2 hours.

Four different catalysts were finished using the extrudate particles andan evaporative impregnation with rhenium metal by using an aqueoussolution of ammonium perrhenate (NH₄ReO₄). The impregnated base wascalcined in air at 540° C. for 2 hours and resulted in a metal level of0.4 wt-% rhenium. Next the catalysts were reduced for 12 hours inhydrogen at 500° C. Then the catalysts were sulfided using an injectionof hydrogen sulfide (H₂S) gas into a mixed sample in a rotating vesselfor even sulfur distribution over the catalyst particles. Catalyst A wasfinished at a molar ratio of sulfur to rhenium of 0.5 mol S/mol Re.Catalyst B was finished at a molar ratio of sulfur to rhenium of 0.8 molS/mol Re. Catalyst D did not undergo sulfiding and thus represented acatalyst of the prior art. Catalyst C did not undergo either sulfidingor the final reduction step for 12 hours; instead it only was reduced inhydrogen for approximately 3 hours.

Example 2

Catalysts A, B, C, and D were tested for aromatics transalkylationability in a pilot plant using an aromatics feed blend of C₇, C₉, andC₁₀ aromatics to demonstrate effectiveness of catalyst presulfiding incontrolling methane production when producing C₈ aromatics. The testconsisted of loading a vertical reactor with catalyst and contacting thefeed at 2860 kPa abs (400 psig) under a space velocity (WHSV) of 2 hr⁻¹and hydrogen to hydrocarbon ratio (H₂/HC) of 4. A conversion level ofabout 50 wt-% of feed aromatics was achieved. FIG. 1 shows the resultson catalyst activity as measured by a weighted average bed temperature,and FIG. 2 shows the results on catalyst methane production as aweighted percentage of light ends that includes C₁ through C₅ compounds.

The data showed that sulfiding of a rhenium containing catalyst servedto reduce the methane production during an aromatics transalkylationreaction. Accordingly, the reduced methane production is understood tobe accompanied by less hydrogen consumption and a lower exothermassociated with reduced metal hydrogenolysis of lighter carbon numbermaterial, and correspondingly improved yields of desired xylene speciesfrom the transalkylation process when operated at lower total hydrogenpartial pressures.

1. A process for preparing a transalkylation catalyst comprisingcontacting the catalyst comprising a rhenium component, a solid-acidcomponent, and an optional binder, with a sulfur-based treating agenteffective for decreasing yields of methane under transalkylationconditions to form a catalyst consisting essentially of a rheniumcomponent, a solid-acid component, an optional binder, and a sulfurcomponent wherein the catalyst mole ratio of sulfur to rhenium is about0.3 to about 0.8 and wherein the solid-acid component is selected fromthe group consisting of: (A) mordenite having a SiO₂/Al₂O₃ ratio fromabout 13 to about 19, and (B) mordenite having a SiO₂/Al₂O₃ ratio fromabout 13 to about 19, in combination with another component selectedfrom the group consisting of mazzite, zeolite beta, ZSM-11, ZSM-12,ZSM-22, ZSM-23, EU-1, MAPO-36, MAPSO-31, SAPO-5, SAPO-11, SAPO-41, MFItopology zeolites, silica-alumina and combinations thereof.
 2. Theprocess of claim 1 wherein the sulfur-based treating agent is selectedfrom the group consisting of carbon disulfide, methylsulfide,dimethylsulfide, dimethyldisulfide, methylethylsulfide, diethylsulfide,dibutylsulfide, and mixtures thereof.
 3. The process of claim 1 whereinthe sulfur-based treating agent is hydrogen sulfide.
 4. The process ofclaim 1 wherein the sulfur-based treating agent is provided in atreating medium comprising from about 10 to about 100 wt-% of thetreating agent.
 5. The process of claim 1 wherein the sulfur-basedtreating agent is provided in a hydrocarbon feed stream medium at alevel above about 0.1 wt-ppm sulfur.
 6. The process of claim 1 whereinthe sulfur-based treating agent is provided in a hydrocarbon feed streammedium at a level ranging from about 100 to about 500 wt.-ppm.
 7. Theprocess of claim 1 wherein the solid-acid component is mordenite havinga SiO₂/Al₂O₃ ratio from about 13 to about
 19. 8. The process of claim 1further comprising the step of reducing the catalyst at a temperaturegreater than about 400° C. in the presence of hydrogen for a time periodgreater than about 2.5 hours.
 9. A catalyst for transalkylation ofaromatics consisting essentially of a rhenium component, a solid-acidcomponent, an optional binder, and a sulfur component wherein thecatalyst mole ratio of sulfur to rhenium is about 0.3 to about 0.8 andwherein the solid-acid component is selected from the group consistingof: (A) mordenite having a SiO₂/Al₂O₃ ratio from about 13 to about 19,and (B) mordenite having a SiO₂/Al₂O₃ ratio from about 13 to about 19,in combination with another component selected from the group consistingof mazzite, zeolite beta, ZSM-11, ZSM-12, ZSM-22, ZSM-23, EU-1, MAPO-36,MAPSO-31, SAPO-5, SAPO-11, SAPO-41, MFI topology zeolites,silica-alumina, and combinations thereof.
 10. The catalyst of claim 9wherein the solid-acid component is mordenite having a SiO₂/Al₂O₃ ratiofrom about 13 to about
 19. 11. The catalyst of claim 9 wherein thebinder is an inorganic oxide component.